1. Field of the Invention
The invention relates in general to an image sensor, and more particularly to an image sensor and a black level calibration method.
2. Description of the Related Art
An image sensor, e.g., a charge-coupling device (CCD) or a complementary metal-oxide-semiconductor (CMOS), is a digital optical sensing element for replacing the conventional film. Active pixels of an image sensor detect different degrees of brightness and wavelengths of light emitted from different objects, and read analog information such as a pixel voltage from data detected. The image sensor then converts the analog information to digital information that can be digitally processed.
An image sensor itself is an energy-consuming (power-consuming) equipment. Accompanied with energy consumption, heat energy is produced to aggravate activities of electrons in a chip material. The heated electronics with continuous movements then generate an electric current to form a so-called black current.
An image sensor ideally has a zero black current. However, in the real world, a black current is nevertheless produced due to various factors, a most significant of which is the heat. When a voltage of the black current is substantially the same as a voltage of a low-intensity light, it is in equivalence that pixels of an image sensor “perceive” an object such that exposure is triggered to present a result on a screen.